1 /* 2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com> 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2, or (at your option) 7 * any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * You should have received a copy of the GNU General Public License 15 * along with this program; see the file COPYING. If not, write to 16 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. 17 */ 18 19 /* 20 * Basic idea behind the notification queue: An fsnotify group (like inotify) 21 * sends the userspace notification about events asynchronously some time after 22 * the event happened. When inotify gets an event it will need to add that 23 * event to the group notify queue. Since a single event might need to be on 24 * multiple group's notification queues we can't add the event directly to each 25 * queue and instead add a small "event_holder" to each queue. This event_holder 26 * has a pointer back to the original event. Since the majority of events are 27 * going to end up on one, and only one, notification queue we embed one 28 * event_holder into each event. This means we have a single allocation instead 29 * of always needing two. If the embedded event_holder is already in use by 30 * another group a new event_holder (from fsnotify_event_holder_cachep) will be 31 * allocated and used. 32 */ 33 34 #include <linux/fs.h> 35 #include <linux/init.h> 36 #include <linux/kernel.h> 37 #include <linux/list.h> 38 #include <linux/module.h> 39 #include <linux/mount.h> 40 #include <linux/mutex.h> 41 #include <linux/namei.h> 42 #include <linux/path.h> 43 #include <linux/slab.h> 44 #include <linux/spinlock.h> 45 46 #include <linux/atomic.h> 47 48 #include <linux/fsnotify_backend.h> 49 #include "fsnotify.h" 50 51 static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0); 52 53 /** 54 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events. 55 * Called from fsnotify_move, which is inlined into filesystem modules. 56 */ 57 u32 fsnotify_get_cookie(void) 58 { 59 return atomic_inc_return(&fsnotify_sync_cookie); 60 } 61 EXPORT_SYMBOL_GPL(fsnotify_get_cookie); 62 63 /* return true if the notify queue is empty, false otherwise */ 64 bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group) 65 { 66 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 67 return list_empty(&group->notification_list) ? true : false; 68 } 69 70 void fsnotify_destroy_event(struct fsnotify_group *group, 71 struct fsnotify_event *event) 72 { 73 /* Overflow events are per-group and we don't want to free them */ 74 if (!event || event->mask == FS_Q_OVERFLOW) 75 return; 76 77 group->ops->free_event(event); 78 } 79 80 /* 81 * Add an event to the group notification queue. The group can later pull this 82 * event off the queue to deal with. The function returns 0 if the event was 83 * added to the queue, 1 if the event was merged with some other queued event, 84 * 2 if the queue of events has overflown. 85 */ 86 int fsnotify_add_notify_event(struct fsnotify_group *group, 87 struct fsnotify_event *event, 88 int (*merge)(struct list_head *, 89 struct fsnotify_event *)) 90 { 91 int ret = 0; 92 struct list_head *list = &group->notification_list; 93 94 pr_debug("%s: group=%p event=%p\n", __func__, group, event); 95 96 mutex_lock(&group->notification_mutex); 97 98 if (group->q_len >= group->max_events) { 99 ret = 2; 100 /* Queue overflow event only if it isn't already queued */ 101 if (!list_empty(&group->overflow_event->list)) { 102 mutex_unlock(&group->notification_mutex); 103 return ret; 104 } 105 event = group->overflow_event; 106 goto queue; 107 } 108 109 if (!list_empty(list) && merge) { 110 ret = merge(list, event); 111 if (ret) { 112 mutex_unlock(&group->notification_mutex); 113 return ret; 114 } 115 } 116 117 queue: 118 group->q_len++; 119 list_add_tail(&event->list, list); 120 mutex_unlock(&group->notification_mutex); 121 122 wake_up(&group->notification_waitq); 123 kill_fasync(&group->fsn_fa, SIGIO, POLL_IN); 124 return ret; 125 } 126 127 /* 128 * Remove and return the first event from the notification list. It is the 129 * responsibility of the caller to destroy the obtained event 130 */ 131 struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group) 132 { 133 struct fsnotify_event *event; 134 135 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 136 137 pr_debug("%s: group=%p\n", __func__, group); 138 139 event = list_first_entry(&group->notification_list, 140 struct fsnotify_event, list); 141 /* 142 * We need to init list head for the case of overflow event so that 143 * check in fsnotify_add_notify_events() works 144 */ 145 list_del_init(&event->list); 146 group->q_len--; 147 148 return event; 149 } 150 151 /* 152 * This will not remove the event, that must be done with fsnotify_remove_notify_event() 153 */ 154 struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group) 155 { 156 BUG_ON(!mutex_is_locked(&group->notification_mutex)); 157 158 return list_first_entry(&group->notification_list, 159 struct fsnotify_event, list); 160 } 161 162 /* 163 * Called when a group is being torn down to clean up any outstanding 164 * event notifications. 165 */ 166 void fsnotify_flush_notify(struct fsnotify_group *group) 167 { 168 struct fsnotify_event *event; 169 170 mutex_lock(&group->notification_mutex); 171 while (!fsnotify_notify_queue_is_empty(group)) { 172 event = fsnotify_remove_notify_event(group); 173 fsnotify_destroy_event(group, event); 174 } 175 mutex_unlock(&group->notification_mutex); 176 } 177 178 /* 179 * fsnotify_create_event - Allocate a new event which will be sent to each 180 * group's handle_event function if the group was interested in this 181 * particular event. 182 * 183 * @inode the inode which is supposed to receive the event (sometimes a 184 * parent of the inode to which the event happened. 185 * @mask what actually happened. 186 * @data pointer to the object which was actually affected 187 * @data_type flag indication if the data is a file, path, inode, nothing... 188 * @name the filename, if available 189 */ 190 void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode, 191 u32 mask) 192 { 193 INIT_LIST_HEAD(&event->list); 194 event->inode = inode; 195 event->mask = mask; 196 } 197